Robotic surgical systems and devices are well suited for use in performing minimally invasive medical procedures, as opposed to conventional techniques that may require large incisions to open the patient's body cavity to provide the surgeon with access to internal organs. For example, a robotic surgical system may be utilized to facilitate imaging, diagnosis, and treatment of tissues which may lie deep within a patient, and which may be preferably accessed only via naturally-occurring pathways such as blood vessels or the gastrointestinal tract.
One such robotic surgical system that may be utilized in a minimally invasive procedure is a robotic catheter system. A robotic catheter system utilizes a robot, external to the patient's body cavity, to insert a catheter through a small incision in a patient's body cavity and guide the catheter to a location of interest. Catheters may be steerable for movement in multiple axes including axial insertion/retraction, axial rotation, and deflection/articulation, which encompasses radial bending in multiple directions. To accomplish steering, one or more pullwires are attached to the distal end of an articulating section of a catheter and extend the length of the catheter. The distal tip of a catheter may then be controlled via the pullwires, i.e., by selectively operating tensioning control elements within the catheter instrument.
Kinematic modeling is utilized to predict catheter tip movement within the patient anatomy. The amount of displacement of a pullwire is generally proportional to the amount of articulation. However, at times the calculated motion of the catheter does not precisely match the actual motion within the patient's anatomy. Various elements can affect the amount of articulation for a given pullwire actuation, including the presence of unanticipated or un-modeled constraints imposed by the patient's anatomy, particularly given the tortuous path that the catheter must traverse. Minimization of differences between actual and predicted kinematic functions is desirable to achieve a highly controllable robotic surgical system.
In known robotic catheter systems, shafts that actuate the pullwires are connected through transmission elements to motors. Each motor is equipped with an encoder. However, the load transmitted to an output shaft, as well as the position of the output shaft, is not known. Additionally, while the position of the output shaft is calculated, the torque applied at the output shaft cannot be precisely calculated because of the variations in transmission efficiency and the effects of perturbations on the system due to catheter construction shape and use. Moreover, external forces on the catheter can change the loading on the catheter pullwires and, for a fixed position of the output shaft, in turn may change the torsion loading on the output shafts.
Accordingly, there is a need for a robotic catheter system and method of using the same that addresses the above problems.